Technical Abstract:
In Yersinia pestis, Y. pseudotuberculosis, and Y, enterocolitica, phenotypic expression of several virulence plasmid (pYV: 70-kb)-associated genetic determinants may include low calcium response (Lcr, pin point colony, size = 0.36 mm), colony morphology (size = 1.13 mm), crystal violet (CV) binding (dark-violet colony), Congo Red (CR) uptake (red pin point colony, size = 0.36 mm), autoagglutination (AA = cells agglutinate), and hydrophobicity (HP = clumping of cells). Y. pseudotuberculosis is chromosomally closely related to Y. pestis, whereas, Y. enterocolitica is chromosomally distantly related to Y. pestis and Y. pseudotuberculosis. All three species demonstrate Lcr, CV binding, and CR-uptake. The colony morphology/size, AA, and HP characteristics are expressed in both Y. pseudotuberculosis and Y. enterocolitica, but not in Y. pestis. Congo red-uptake in Y. pestis was demonstrated only on calcium-deficient CR magnesium oxalate tryptic soy agar (CRMOX), whereas this phenotype was expressed on both CRMOX and low-calcium agarose media in Y. pseudotuberculosis and Y. enterocolitica. These phenotypes were detectable at 37 degrees C within 24 h in Y. enterocolitica and Y. pseudotuberculosis, but did not appear until 48 h in Y. pestis due to its slower growth rate at 37 degrees C. The pYV is unstable in all three species but is more unstable in Y. pestis. The specific CR-uptake by Y. pestis in CRMOX and the delayed time interval to express Lcr and CR-uptake provide the means to differentiate Y. pestis from Y. enterocolitica and Y. pseudotuberculosis. These differences in pYV expression in Y. pestis can be used in its isolation and detection from food.